Staphylococcus aureus: Difference between revisions

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Staphylococcus aureus
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== Background ==
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==Background==
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=== Microbiology ===
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===Microbiology===
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* Facultative anaerobic, [[Stain::Gram-positive]] coccus
  
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* [[Catalase test::Catalase-positive]] and [[Has coagulase test::coagulase-positive]]
  
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* Microscopy: groups or clusters ("cluster of grapes")
  
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* Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar
  
   
  +
*Facultative anaerobic, [[Stain::Gram-positive]] [[Shape::coccus]]
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=== Pathophysiology ===
  
  +
*Catalase-[[Catalase::positive]] and coagulase-[[Coagulase::positive]]
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==== Virulence factors ====
  
  +
*Microscopy: groups or clusters ("cluster of grapes")
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* Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
  
  +
*Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar
−
* Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL)
  
−
* Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome
  
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* Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines
  
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** Toxic shock syndrome toxin 1 (TSST-1) is implicated in [[TSS|Staphylococcal toxic shock syndrome]]
  
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** Exotoxins B and C cause [[TSS|Staphylococcal toxic shock syndrome]] and also food poisoning
  
   
  +
===Pathophysiology===
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==== Antibiotic resistance ====
  
  +
====Virulence Factors====
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* Mechanisms of resistance are myriad
  
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* Two common ones:
  
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** ''bla'' gene encodes penicillinase, conferring resistance to penicillin
  
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** ''mecA'' encodes PBP2a, conferring broad beta-lactam resistance
  
   
  +
*Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
−
== Clinical Manifestations ==
  
  +
*Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL)
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=== Colonization ===
  
  +
*Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome
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* About 20-30% of people carry it in their nares
  
  +
*Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines
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* See [[Staphylococcus aureus decolonization]]
  
  +
**Toxic shock syndrome toxin 1 (TSST-1) is implicated in [[TSS|Staphylococcal toxic shock syndrome]]
  +
**Exotoxins B and C cause [[TSS|Staphylococcal toxic shock syndrome]] and also food poisoning
   
  +
====Antibiotic Resistance====
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=== Skin and soft tissue infections ===
  
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* Boils and carbuncles
  
   
  +
*Mechanisms of resistance are myriad
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=== Scalded-skin syndrome ===
  
  +
*Common ones:
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* Aka Ritter disease
  
  +
**''bla'' gene encodes penicillinase, conferring resistance to penicillin
−
* Caused by exfoliative toxin A or B
  
  +
**''mecA'' encodes PBP2a, conferring broad β-lactam resistance (MRSA)
−
* Essentially bullous impetigo
  
  +
**''vanA'' on a plasmid confers [[vancomycin]] resistance (VRSA)
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* Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)
  
   
  +
==Clinical Manifestations==
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=== Bacteremia ===
  
  +
===Colonization===
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* See [[Staphylococcus aureus bacteremia]]
  
   
  +
*About 20-30% of people carry it in their nares
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=== Infective endocarditis ===
  
  +
*See [[Staphylococcus aureus decolonization]]
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* Usually more acute presentation
  
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* High mortality
  
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* See [[Staphylococcus aureus endocarditis]]
  
   
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=== Myriad other infections ===
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===Skin and Soft Tissue Infections===
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* Osteomyelitis
  
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* Native and prosthetic joint infections
  
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* Pyomyositis
  
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* Deep organ abscesses
  
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* Surgical site infections
  
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* Pneumonia, especially ventilator-associated or influenza-related
  
   
  +
*Boils and carbuncles
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=== Superantigen-related syndromes ===
  
  +
*Cellulitis, usually purulent
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* Food poisoning
  
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* [[Staphylococcal toxic shock syndrome]]
  
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** Tampon-associated
  
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** Post-surgical (ENT): more of historic with changes in packing
  
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** Surgical site infections, even without obvious signs of localized infection
  
   
  +
===Scalded-Skin Syndrome===
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== Management ==
  
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* Duration depends on clinical syndrome
  
   
  +
*Aka Ritter disease
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=== Methicillin-susceptible ''Staphylococcus aureus'' (MSSA) ===
  
  +
*Caused by exfoliative toxin A or B
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* First-line: [[cloxacillin]], then [[cefazolin]] or [[cephalexin]] (for oral)
  
  +
*Essentially bullous impetigo
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* Others: [[clindamycin]], [[fluoroquinolones]], [[TMP-SMX]], [[doxyxycline]], [[erythromycin]]
  
  +
*Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)
   
  +
===Bacteremia===
−
=== Methicillin-resistant ''Staphylococcus aureus'' (MRSA) ===
  
  +
−
* First-line: [[vancomycin]]
  
  +
*See [[Staphylococcus aureus bacteremia]]
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* Others: [[linezolid]] (if lungs) and [[daptomycin]] (if blood), but also consider [[TMP-SMX]], [[ciprofloxacin]], [[doxycycline]], and [[clindamycin]]
  
  +
  +
===Infective Endocarditis===
  +
  +
*Usually more acute presentation
  +
*High mortality
  +
*See [[Staphylococcus aureus endocarditis]]
  +
  +
===Other Infectious Syndromes===
  +
  +
*[[Osteomyelitis]]
  +
*[[Septic arthritis|Native]] and [[prosthetic joint infection]]
  +
*[[Pyomyositis]]
  +
*Deep organ [[abscess]]
  +
*[[Surgical site infection]]
  +
*[[Pneumonia]], especially ventilator-associated or influenza-related
  +
  +
===Superantigen-Related Syndromes===
  +
  +
*[[Food poisoning]]
  +
*[[Staphylococcal toxic shock syndrome]]
  +
**Classically tampon-associated
  +
**Post-surgical (ENT): more of historic with changes in packing
  +
**Surgical site infections, even without obvious signs of localized infection
  +
  +
=== ''Staphylococcus''-Associated Glomerulonephritis ===
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  +
* Occurs ''during'' acute infection
  +
* See also [[Staphylococcus-associated glomerulonephritis]]
  +
  +
==Management==
  +
  +
*Duration depends on clinical syndrome
  +
  +
===Methicillin-Susceptible ''Staphylococcus aureus'' (MSSA)===
  +
  +
*First-line: [[cloxacillin]], then [[cefazolin]] or [[cephalexin]] (for oral)
  +
*Others: [[clindamycin]], [[fluoroquinolones]], [[TMP-SMX]], [[doxyxycline]], [[erythromycin]]
  +
  +
===Methicillin-Resistant ''Staphylococcus aureus'' (MRSA)===
  +
  +
*First-line: [[vancomycin]]
  +
*Others: [[linezolid]] (if lungs) and [[daptomycin]] (if blood), but also consider [[TMP-SMX]], [[ciprofloxacin]], [[doxycycline]], and [[clindamycin]]
   
 
{{DISPLAYTITLE:''Staphylococcus aureus''}}
  
{{DISPLAYTITLE:''Staphylococcus aureus''}}

Latest revision as of 20:50, 21 February 2021

Background

Microbiology

  • Facultative anaerobic, Gram-positive coccus
  • Catalase-positive and coagulase-positive
  • Microscopy: groups or clusters ("cluster of grapes")
  • Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar

Pathophysiology

Virulence Factors

  • Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
  • Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL)
  • Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome
  • Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines

Antibiotic Resistance

  • Mechanisms of resistance are myriad
  • Common ones:
    • bla gene encodes penicillinase, conferring resistance to penicillin
    • mecA encodes PBP2a, conferring broad β-lactam resistance (MRSA)
    • vanA on a plasmid confers vancomycin resistance (VRSA)

Clinical Manifestations

Colonization

Skin and Soft Tissue Infections

  • Boils and carbuncles
  • Cellulitis, usually purulent

Scalded-Skin Syndrome

  • Aka Ritter disease
  • Caused by exfoliative toxin A or B
  • Essentially bullous impetigo
  • Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)

Bacteremia

Infective Endocarditis

Other Infectious Syndromes

Superantigen-Related Syndromes

Staphylococcus-Associated Glomerulonephritis

Management

  • Duration depends on clinical syndrome

Methicillin-Susceptible Staphylococcus aureus (MSSA)

Methicillin-Resistant Staphylococcus aureus (MRSA)

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